During the production of the pesticide lindane (γ-hexachlorocyclohexane; γ-HCH), large quantities of
byproducts, like the α-, β-, and δ-HCH isomers,
were discarded at dump sites. β-HCH was found to
be extremely persistent in the environment under
aerobic conditions. We studied the degradation of
this
isomer under methanogenic conditions in a flow-through column packed with polluted sediment. β-HCH
was completely removed in this system. Chlorobenzene was detected in the effluent as a product. A
β-HCH transforming anaerobic enrichment culture was
obtained in batch cultures by using the column
material as inoculum.
δ-2,3,4,5-Tetrachlorocyclohexene
is proposed as an intermediate during transformation,
while benzene and chlorobenzene were formed as
stable end products. The enrichment culture was also
able to dechlorinate α-HCH at a comparable rate
and γ- and δ-HCH at lower rates. Dechlorination
was
inhibited by the addition of vancomycin, but not by
the addition of bromoethanesulfonic acid.
Pasteurization
inhibited dechlorination completely. This is the
first
detailed description of the biodegradation of β-HCH,
including intermediate and end product identification,
under defined anaerobic conditions.